Abstract

The turbine blade had failed by fatigue. The fatigue crack had initiated at the trailing edge and propagated progressively towards the leading edge before culminating in final overload failure. The fatigue crack origin was found to have a post fracture damage and hence no direct evidences were available for establishing the reason for fatigue crack initiation. However, investigation revealed that the airfoil surfaces of all the blades were covered with a thick layer of SiO2 particles. This is possible only when the steam is contaminated with SiO2 particles. In view of this, foreign object damage appears to be one of the possible reasons for fatigue crack initiation. No mechanical and/or metallurgical abnormalities were responsible for the fatigue failure of the blade.